ERROR CudafyHostException Data ist not on the device

Hallo, at the moment i try to get a feeling for using cudafy.
I simply want to copy a float array to the device (Geforce GT 630), do a simple calculation and copy it back to the host, I read the examples and coded it the same way.

while running the code i get the error CudafyHostException Data is not on the device (gpu.CopyFromDevice(GPUdat, gpu_dat);).
And i realy dont understand why. The examples run perfect on my system and i think i did the same.